Antenna



- J. H. ROE

June 13, 1950 ANTENNA Filed June 28, 1946 INVENTOR JOHN H. ROE

TRANSMISSION L INE Patented June 13, 1950 ANTENNA John H. Roe, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 28, 1946, Serial No. 679,946

4 Claims.

The present invention relates to antennas and more particularly to wide band antennas for use at ultra high frequencies for airborne equipment.

An object of the present invention is the provision of a broad band antenna for use on highspeed airplanes.

Another object of the present invention is to provide an aircraft antenna having a band width of the order of one octave.

Still another object of the present invention is the provision of a vertical quarter wave radiator which has a band width substantially independent of the shape or size of the ground plane upon which it is mounted.

A further object f the present invention is the provision of a broad band antenna which does not require stubs or other matching networks for feeding the antenna from a 50 ohm coaxial line.

Still a further object of the present invention is the provision of a vertical stub aircraft antenna which is simple in mechanical construction and strong enough to withstand high flying speeds.

Another object of the present invention is to provide a form of construction of aircraft antenna which will increase the strength of the antenna.

The foregoing objects and others which may appear from the following detailed description are attained by providing a vertical stub antenna of large cross section and about a quarter wavelength long at the center frequency of the band. The radiator is streamlined in cross section and adapted to be mounted normal to the exterior metal surface of a metal airplane. The antenna is hollow and contains a tie rod running from the free end to the ground plane and connected to the antenna and to the ground plane. The tie rod acts as a shunt inductance across the input f the antenna, thus causing an increase in the band width of the antenna.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which:

Figure 1 illustrates partly in section an elevational view of the antenna, while Figure 2 illustrates a transverse section of the antenna of Figure 1 taken along lines 2, 2.

Referring now t Figure 1 I have shown mounted normally to the conductive ground plane GP a radiator element Ill. The conductive ground plane may be the outer surface of the fuselage of an airplane or of the wing of the airplane. This radiator is in the form of a hollow streamlined tube slightly less than one quarter of the operating wavelength in length. The tube itself may be made of a standard tear-drop, airfoil section of steel tubing. For a band of frequencies centered at approximately 320 megacycles, the tube may be approximately 9.2 inches long. It may have a major axis of about 4 inches, which is somewhat less than the one eighth of the operating wavelength, and a minor axis of about 1 inches. For other ranges of frequencies, it is important to maintain approximately the same ratio of cross sectional dimensions to height. The space between lower end of radiator l0 and ground plane GP is also an important factor. The effect of this space varies somewhat depending upon whether the space is open or whether, as is shown in the drawing, it is filled with a solid dielectric material such as insulator I2. The radiator element I0 is maintained in position by tie rods I4 and 20 secured to upper closing plate l8, passing through the length of radiator ll] through insulator l2 and ground plane GP. The antenna may be energized by connecting the outer conductor of a standard 50 ohm coaxial transmission line to the ground plane GP and the inner conductor to the lower end of tie rod l4. Tie rod [4 is insulated from ground plane GP by washer l5 but is electrically connected to radiator H! at its lower end by its contact with the lower closing plate I6. Tie rod 20, extending from the upper end l8 of the radiator insulated from the lower plate 16 by washer l1 and connected to ground plane GP, acts eflfectively as a shunt impedance across the input of the antenna. At the low frequency end of the band the shunt impedance is essentially inductive in nature. Since the antenna normally has a capacitative reactance at this end of the band, the input impedance is increased at this end of the band and an effective increase in band width is attained. Mechanically the tie rod 20 provides an additional means of support for radiator 10 and thus increases the strength of the antenna.

If we adopt the commonly accepted limit of mismatch of 33% reflection coefficient, corresponding to a 2:1 standing wave ratio on the transmission line, then the band width of antenna herein shown and described is of the order of one octave and within reasonable limits is independent of the shape or size of the ground plane GP.

While I have illustrated a particular embodiment of the present invention, it should be 3 clearly understood that it is not limited thereto since many modifications may be made in the several elements employed and in their arrangement without departing from the spirit and scope of the invention.

What is claimed is:

1. An aircraft antenna for use with an element affording a conductive ground plane and including a radiator in the form of a hollow tube mounted normal to the conductive ground plane, insulation means spacing the lower end of said tube from said ground plane, a pair of tie rods connected to the upper end of said tube and passing through the length of said tube and through said ground plane, one of said tie rods being connected to said ground plane and the other being insulated therefrom, said other rod being connected to the lower end of said tube and means for coupling a transmission line to said ground plane and said other tie rod.

2. An aircraft antenna including an element affording a conductive ground plane, a radiator in the form of a hollow tube mounted normal to a conductive ground plane, said tube having a length substantially one quarter of the operating wavelength, insulation means spacing the lower end of said tube from said ground plane, a pair of tie rods connected to the upper end of said tube and passing through the length of said tube and through said ground plane, one of said tie rods being connected to said ground plane and the other bein insulated therefrom, said other rod being connected to the lower end of said tube, and means for coupling a transmission line to said ground plane and said other tie rod.

3. An aircraft antenna for use with an element affording a conductive ground plane and including a radiator in the form of a hollow tube mounted normal to a conductive ground plane, insulation means spacing the lower end of said tube from said ground plane, a pair of tie rods connected to the upper end of said tube and passing through the length of said tube and through said ground plane, one of said tie rods being connected to said ground plane and the other being insulated therefrom, said other rod being connected to the lower end of said tube, and means for coupling a transmission line to said ground plane and said other tie rod, said tube having a streamlined cross section.

4. An aircraft antenna including an element affording a conductive ground plane, a radiator in the form of a hollow tube mounted normal to a conductive ground plane, said tube having a length substantially one quarter of the operating wavelength, insulation means spacing the lower end of said tube from said ground plane, a pair of tie rods connected to the upper end of said tube and passing through the length of said tube and through said ground plane, one of said tie rods being connected to said ground plane and the other being insulated therefrom, said other rod being connected to the lower end of said tube, and means for coupling a transmission line to said ground plane and said other tie rod, said tube having a streamlined cross section.

JOHN H. ROE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,786,631 Roe Dec. 30, 1930 2,201,857 Dome May 21, 1940 2,313,046 Bruce Mar. 9, 1943 2,321,454 Brown June 8, 1943 2,35 ,314 Harsted July 25, 1944 2,463,547 Meier Mar. 8, 1949 

